Multi-pump system having speed and pressure rise responsive by-pass means



W. E. FORTMANN MULTI-PUMP SYSTEM HAVING SPEED AND PRESSURE Filed Oct. 3, 1957 COMP/95550@ f// M6/N5 -1 5,0550 I PAQ/40105756 i Af VM.

MULTI-PUMP SYSTEM HAVING SPEED AND lli/IIESSISJRE RISE RESPONSIVE BY-PASS AN William E. Fortmann, Farmington, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Oct. 3, 1957, Ser. No. 688,016

3 Claims. (Cl. 15S-36.4)

This invention relates to fluid supply systems for powerplants and more particularly to fluid systems for aircraft engines to permit adequate and efficient fuid distribution Vto the powerplant at all altitudes.

It is an object of this invention to teach a fluid supply System, such as a fuel supply system for an aircraft engine, which utilizes two pumps in parallel and has a by-pass provision for one such pump so that both pumps are operable during engine starting and so that but one pump is operable during all other normal engine operations.

It is a further object of this invention to provide a multi-pump system in which anauxiliarypump is activated when the normal pump fails.

It is still a further object of this invention to teach a fuel supply system for modern aircraft engines comprising a main and an auxiliary pump and having an auxiliary pump by-pass system which is operable when both engine speed and main pump pressure rise exceed preselected limits and which becomes inoperative when either engine speed or main pump pressure reduces below these preselected limits.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is an external showing of a modern turbojet type of aircraft engine or powerplant with schematic illustrations of a fuel control and fuel pump system attached thereto.

Fig. 2 is a schematic representation of my fuel pump system and a portion of a fuel control system.

Referring to Fig. l, we see a modern turbojet aircraft engine which comprises air inlet section 12, compressor section 14, burner section 16, turbine section 18, and exhaust nozzle section 20, which culminates in exhaust outlet 22. Air is introduced to engine 10 through inlet section 12 and is compressed when passing through compressor section 14 and is then heated in passing through burner section 16. Power to drive the compressor is extracted from the heated and compressed air in turbine section 18 and, after passing through turbine section 18 and exhaust nozzle section 20, the heated and compressed powerplant gases are discharged to atmosphere through exhaust outlet 22 in a thrust generating function. Fuel is introduced to fuel nozzles 24, which are located within engine burner section 16, from fuel pump System 30 after first being regulated in quantity flow by fuel control unit 26. Fuel control unit 26 provides fuel to engine 10 through fuel nozzles 24 in quantity dictated by engine parameters such as engine speed, compressor inlet temperature, and compressor outlet pressure, among others, and pilot lever 32 in well-known fashion as is more particularly shown and described in United States Patent Numbers 2,759,549, 2,782,767, and 2,782,769 to which reference may be had to a more particular description of fuel control unit 26.

Now referring to Fig. 2, we see our uid or fuel supply system 30 in combination with portions of fuel control unit 26 coacting to supply a fluid such as engine fuel to the powerplant, such as aircraft engine 10, by way of p conduit 34. Fuel control unit 26 is schematically illustrated to be sensitive to compressor discharge pressure P31 engine speed and temperature and performs the function of varying the fuel flow through throttle valve unlt 35, by positioning throttle valve 36 with respect toY throttle valve seat 37 so as to define the area and hence the ow through throttle valve orifice 38. Our fuel supply' system 30 performs the function of supplying fuel to be passed through throttle valve unit 35 and includes the main components of main or normal fuel pump 40, auxiliary or stand-by fuel pump 42, by-pass valve 44 andVV 40 or through line 52 to auxiliary pump 42. Spring S8v biases by-pass piston 60 of by-pass valve 44 toward its closed position.

After passing through auxiliary pump 42, the fuel will thn be passed either through conduit 62 to by-pass valve 44, from whence it will return through line 54 to inlet conduit 48 when by-passed valve piston 60 is in its open or far right position. If by-pass valve 44 is closed, the discharge pressure from auxiliary pump 42 will lift check valve 64 against the urgings of spring 66 as well as the pressure in line 68 and provide fuel through lines 68 and 70 to throttle valve unit 35.

After passing through main pump 40, fuel may passV either through line 72 after lifting check valve 74 against the urging of spring 76 as well as the pressure in liney 68 to join the ow of fuel from auxiliary pump 40 in line 70 to throttle valve unit 35 or pass through line4 78 to speed sensing unit 46 and, when sensing unit 46 isl in its open position, through line 80 to the anti-spring side of by-pass valve piston 60. Speed sensing unit 46 is of the piston valve or spool type and is driven through rod 82 and intermeshing gears 84 and 86 either at the speed of engine 10 or as some function of the speed of engine 10. Speed sensitive flyball unit is carried by spool unit 92 of sensing system 46 and serves the function of shifting spool 92 rightwardly against the urging of ad-r, justable spring 94 when engine speed or the engine speedv parameter exceeds a preselected limit. This rightward shifting of spool 92 puts conduits V78 and 80 into cornmunication so that the discharge side 96 of main pumpl 40 is communicating with the anti-spring side 98 of bypass valve 44.

By-pass pressure regulator unit 100 is provided to regulate the pressure of the fuel provided to throttle valve unit 35.

By observing Fig. 2, it will be noted that fuel will be passed to the powerplant from both main pump 40 andv auxiliary pump 42 when either the speed of engine 10V or the pressure rise across main pump 40 are below preselected limits, for either will disable by-pass valve 44. Fuel will be provided to engine 10 from main pump 40. only when both the speed of engine 10 and the pressure rise across main fuel pump 40 exceed a predetermined limit, for both must occur to actuate by-pass valve 44 and cause auxiliary pump A42 to by-pass back to inlet conduit 48.

Operation Patented Jan. 17, V1961v main fuel pump 40 and auxiliary fuel pump 42 will increase and if it were not for the inclusionY of engine speed responsive sensing 46, the pressure rise across main fuel pump,.40fcouldbecomesuieient to actuateby-pass .valve 44. and, putgauxiliary,pump- 42,off the line before the engine.hasattainedsuicient speedthat the `fuel output of mainfuel pump, 4()V aloneatisfies therequirements of enginel. SinceV engine .would be unable to increase 1nspeedproperly without an, adequate fuel supply, the operation of by-.passvalve 44rasa function of main pump pressurerise solely, especially when a low pressure'rise is selected as the actuating. limit of by-pass valve 44, would not bedesirable. It is aY teaching of this invention to .use somemeanssuch as servo mechanism 46 which is responsiveto enginespeed or some engineparameter indicative-of engine speed without respect to engine altitude to,disable,by.pass valve 44` untilv the engine speed increases to. apoint where the-speed and. hence theoutput of main fuel pump 40` would-.be suficientfor powerplant use. Assuming-,thatmain pump 40 generates a-suflicient pressuretrisethereacross to activate by-pass valve 44, such will not occur until, but will occur when theV speed of engine 10 reaches a vpreselected minimum limit, whereupon spool. 92 of servo mechanism 46 will shift to the right, as shownin Fig. 2,'. to providemain pump discharge pressure through line 80,4 to theanti-spring side of by-pass valve piston.60 main pump` inlet pressure already being in cavity 56,011 the spring biased sideof by-pass valve piston 60. At this point,.since both our engine speed and main pump pressure rise are above the` preselected limitsfor each, auxiliary pump 42 is by-passing through line, 54 thereby redueingjhe,heat-,generated in the. fuel caused by the operation ofauxiliarypump 42 in addition to main pump 40.A If main pump-40 should malfunction, such that the pressure rise thereacross would be insufficient to provide adequate quantities of fuel to engine 10, by-pass valve 44 wouldclose in response tomain pump pressure rise reductionand ,thereby put auxiliary pump 42 back on the line Vto provide fuel yto engine 10. In theV same fashion, iii-,engine Aspeed is reduced below a preselected minimum, fiyballs 90 would swing inwardly to shift spool 92 to the left, as shown in Fig.V 2, and thereby disable by-pass valve 44so that both main pump 40 and auxiliary pump 42 are on ,the line'to insurean adequate fuel supply to engine 10,at the high leakage low speed operation. Accordingly, the reduction of either main pump pressure rise or engine speed belowpreselected limits will disable by-Dass valve 40 and place. auxiliary pump 42 back on the line.

If,`in an effort to eliminate the need for engine speed responsive servo 46, the actuation limit of by-pass valve 44'was set sufficiently high that the necessary assistance of auxiliary fuel pump. 42 would not be lost during the starting operation, it would be found that the pressure rise across main pump 40 would be insufficient at altitude to overcome spring 58 so that by-pass valve 44 would be closed and this would place auxiliary pump 42 on'the line at all times at altitude` thereby causing unnecessary heat generation Within the fuel by inefticiently supplying more than enough fuel for proper powerplant operation. The reduced pressure rise of fuel across main pump 40 at altitude is due to the expansion ofthe entrapped air in the fuel due to reduction in atmospheric pressure and the attendant reduction in pumping efficiency. Further, the aforementionedtrarified atmosphere will reduce the pressure in the burner and the burner fuel requirement so that the fuel ow is accordingly reduced as is the pressure drop across the fuel nozzle and, hence, the pressure rise across the vmain-fuel pump 40.

While, for the-purposeof simplifying explanation, enginespeedhas been` shown as aby-pass disabling parameter, it should be-understoodthat any parameter indicative-of'engine-speedfand'independent of altitude, for instance, the pressure ratio across the engine compressor 14v could-as well asv be used and comes within the spirit ofA this .ilu/endort.y

It is to be understood that the invention is not limited to the specific embodiment herein illustrated andv described but may be used in ofher ways without departure from its spirit as defined by the following claims.

I claim:

1. In a powerplant fluidsupplylsystem, a main and an auxiliary fluid pumpA in parallel, a. by-pass piston, type valve for saidV auxiliary pump which by-passvalve is spring biased toward closed, said by-pass valve' being actuated by the pressure rise across said main pump by being subjected to main pump inlet pressurefon one piston side and main pump discharge` pressure on the anti-spring side of said piston, and a servo valve shiftable in response to powerplant'speed to interrupt the admission of main pump discharge pressure to said by-pass valve to permit said spring to close said by-pass valve.

2. In a powerplant fluid supply system, a main and an auxiliary fiuid pump in parallel, a normallyy force biased closed by-pass piston type valve for said auxiliary pump, said by-pass valve being ,actuated to an open position by the pressure rise across said main pump sufiicient to overcome the closing biasing force byb'eing subjected to main pump inlet pressure on one piston side and main pump discharge pressure on the other piston. side, and powerplant speed responsive means to interrupt main pump discharge pressure to said valve andy thereby close said bypass valve to prevent flow through said by-pass valve and cause bothof said pumps to simultaneously provide fluid to said powerplant when powerplant speed is below a predetermined limit so that both of said pumps simultaneously provide fiuid to said powerplant when the pressurerise across said main pump; is below a preselected limit and when said powerplant speed is below a preselected limit.v

3.v An aircraft engine, a fluidI supply system for said engine, a main and an auxiliary fluid pump in parallel' with each of 'said pumps having an inlet and a discharge side, first means to supply fluid to said pumps, second means to conduct the fluid from said pumps to said en,-

gine, a first conduit connecting the-discharge side of saidV auxiliary pump to said first means, a by-pass valve of the piston type located in and adapted to block said first con-l duit whenV closed and which by-pass valve is spring biased toward closed, a secondV conduit to connect said main' pump discharge side to one side of said by-pass valve, a

third conduit to connect saidfirst means to the springside of said 'by-pass valve so that said by-pass valve will be opened in response to pressure rise across said main pump in excess of a predetermined value thereby causingy said auxiliary pump to by-pass, and a servo valve located in said second conduit and shiftable inl response to engine speedto a first position to permit the admission of main pump discharge pressure to said by-pass valve when engine speed exceeds a preselected value to permit said bypassvalve to actuate and cause said auxiliary pump'to by-pass when both engine speed and main pump, pressurev rise are'above preselected limits and which servo valve is shiftable to a second position to block the admission ofA main pump discharge pressure to said by-pass valve when engine speed is below a preselected limit to thereby prevent fiow through said by-pass valve and cause by-pass of said auxiliary pump to cause said auxiliary pump to discharge into said second means.

References Cited in the le of this patent UNITED STATES PATENTSv 

